Subsurface formation analysis has enabled more efficient oil and gas recovery over the past several decades. One of the important features of a formation necessary for maximum oil and gas recovery is an understanding of its fracture systems. Formation fracture systems may be naturally occurring or a result of activities such as drilling or hydraulic fracturing operations. An understanding of formation fracture properties may, among other uses, facilitate recovery of hydrocarbons, prediction of future fractures, computation of optimum drilling directions, and data necessary for reservoir simulation.
There are currently several tools and methods for gathering acoustic data and methods for imaging fractures using a separate analysis remote from the wellsite. In these situations, the time delay between when data acquisition and when fracture imaging can be disadvantageous to operators. Thus the ability to image a subsurface fracture at the wellsite is desirable. Further the ability to perform a quality control check on data while still at the wellsite offers operational advantages. In addition, a fracture image generated at the wellsite can be a useful comparison to a fracture image generated by remote analysis to build confidence or suggest further investigation depending on the coherency of the separate images.
Nevertheless, imaging techniques require additional CPU usage, which is often at a premium at the wellsite. It is desirable for computation speed to be fast, but also for CPU usage to be light, so that imaging fractures does not affect the data acquisition associated with formation evaluation.
Data for generating images of a fracture or other formation features are often provided from acoustic tools. A primary use of borehole acoustic measurements is the estimation of Compressional (P) and/or shear (S) wave formation slowness. The estimation of compressional and/or shear wave formation slowness is often expressed as an ST (slowness vs. time) plane and can be visualized at the wellsite with current technology. However, present methods do not fully utilize the ST plane. Therefore, the present invention contemplates making use of the ST plane for imaging a fracture.